1. Field of the Invention
This invention relates to a process for removing gels from polymer solutions, and in paticular, cellulose ester solutions.
2. Description of the Prior Art
When polymers are dissolved in solvents to form spinning solutions, it is commonly found that the solution contains small gels which are objectionable from a quality standpoint. Such gels are usually caused by impurities in the polymer. For example, in cellulose esters such as cellulose acetate, there are frequently very small quantities of cellulose triacetate present. When the cellulose acetate is dissolved in a conventional solvent such as acetone prior to being spun into fibers, the cellulose triacetate present as an impurity is not soluble in the acetone, but instead forms a gel. Such gels, if not removed, may block spinnerette holes, or if they pass through the spinnerette holes, objectionable flaws in products such as fibers may result from the presence of the cellulose triacetate.
In the past, various types of filters have been used in attempts to remove these gels. It has now been discovered, however, that filtering the solution is not an effective means for removing the gels, because many gels will break up into fragments tiny enough to pass through the filter and agglommerate to form new gels downstream from the filter.
It is also well known, of course, that various types of relatively heavy masses may be separated from lighter liquids by centrifuging batches of the liquid containing the heavier masses.